Introduction
Neotectonic studies the dynamic processes affecting the formation of the earth and the landscapes in it (Keller and Pinter, 2002). In this regard, morphotectonic indices can be used to study tectonic activity in a short time and be used in more detailed future research. Morphotectonics is the knowledge of the study of shapes and shapes created on the earth created by tectonic mechanisms and is interpreted to mean the application of morphological principles in the analysis of tectonic problems (Burbank and Anderson, 2012; Grohmann, 2004; Rangzan et al., 2003). Examining the drainage pattern, and the rate of digging and diversion of rivers provides important information about the expansion and structural evolution of the region (Keller et al., 1998). Pardis city in the Central Alborz tectonic zone is affected by main faults such as the Alborz faults, Mosha fault, and North Tehran fault. Today's earthquakes in Tehran province are a sign of the continuation of the pressure regime prevailing in the province, and the city of Pardis is no exception. The study area has not been studied based on the qualitative indicators of morphotectonics and remote sensing, so it is necessary to predict the conditions and changes in the future of this study. The general purpose of this study is to investigate the seismicity of Pardis city based on qualitative indicators of tectonics and remote sensing for the first time.
Study Area
Pardis city has geographical coordinates of 35 ° 44′22 ″ N, 51 ° 46′40 ″ E, which is located on the slopes of Central Alborz. The geological structure of the study area is studied under the characteristics of the south-central Alborz zone. The existence of multiple fault systems and drift, an outcrop of older rocks, and disturbance of stratigraphic order are the geological characteristics of this region so that in the vicinity of Eocene volcanic sediments (green tuffs of Karaj Formation), shale and coal rocks are formed. Shemshak belongs to the Upper Triassic and Jurassic periods.
Data Analysis
In order to make connections between structural elements such as lines and faults, remote sensing studies have been performed, such as automatic extraction of lines, fractures, and preparation of density maps of lines. ASTER satellite image was used to extract the lines linearly and a linear density map was drawn in Arc GIS software. Rockwork 2016 software has been used to analyze the orientation of fractures and lines as well as faults in the study area. Using Google Earth images and Corel draw software, some tectonic morphology indices such as cone coefficient index, triangular surface index, and canal displacement index have been measured. Using field operations, the geological units and the main structures of the region, which include faults and folds of the region, were investigated.
Results and Discussion
The scattering of the linear indicates that most of the areas that correspond to the faults of the region as high density and in most of the basins there are areas with high density. Changes in magnetic intensity in the study area from northeast to southwest have gradually decreased and the increase in magnetic intensity from south to northwest is due to the proximity of the northern regions to Damavand and the increase of intrusive masses in this region. The study of the risk of surface rupture in Pardis city shows that the bed of this city hosts important faults such as Pardis, Hesa, and Ferdows faults that have cut Quaternary deposits and unfortunately their privacy has not been observed. The earthquakes occurred under the faults of Rudehen, Pardis, and Ferdows. In this area, alluvial fans have been exposed to more destruction due to tectonic and erosive activities and have been removed from the ideal alluvial fan shape. Shows the position of triangular surfaces in the southwest and northwest of the study area at the fault line. Adaptation and comparison of the location of faults and waterway lines in most parts of the region indicate a change in the direction of the tributaries of the waterway network.
Conclusion
Among the important faults in the region are the Rudehen fault, Pardis fault, Ferdows fault, Hesa fault, and North Tehran fault. In addition, the Rudehen fault at a distance of three kilometers north of the city limits, the North Tehran fault, and the Mosha fault can be the causes of destructive earthquakes in this city. The qualitative value of tectonic morphological indices of Pardis city such as alluvial fan index coefficient, triangular surfaces, and sudden changes in the course of rivers indicate the performance of faults and are evidence of the active tectonics of faults in the region. Reinforcement of important buildings and structures such as bridges and highways and reconstruction of worn-out structures is a very important task and should be given priority.